This invention is in the field of devices for the treatment of neurological disorders in human subjects, particularly those disorders that originate in the brain.
The current state of the art in treating neurological disorders such as epilepsy or Parkinson""s disease involves either drugs, destructive nigral lesions or the open-loop electrical stimulation of neurological tissue. Drug therapy has been shown to have significant short and long-term side effects and is often ineffective. In U.S. Pat. No. 3,850,161, Liss describes a continuous closed-loop feedback system which will always feedback part of the brain EEG signal to separate electrodes so that if a large EEG signal occurs it will be fed back in an attempt to cancel out the original signal. This system does not take advantage of recently developed digital signal processing and microcomputer technology by which feedback signals can be activated only when a neurological event occurs, nor does it provide a practical way to recognize and intervene during early stages in the evolution of a neurological event. In addition, the Liss device is not programmable and it does not provide any capability to record EEG signals. Examples of a xe2x80x9cneurological eventxe2x80x9d are the occurrence of an epileptic seizure, a tremor or the occurrence of a migraine aura or migraine headache. A xe2x80x9cneurological eventxe2x80x9d is defined herein as either the precursor of an event such as an epileptic seizure, or the event itself. This concept of detecting an electrical precursor that is a first type of neurological event that occurs some time before the xe2x80x9crealxe2x80x9d event (i.e. anomalous brain electrical activity or a particular pattern of neural activity associated with clinical symptoms) is an important aspect of the present invention. It has been shown that both epileptic seizures and Parkinson""s tremors have precursors that occur before and can be used to predict the onset of the clinical symptom. It is also very likely that other neurological events such as migraine headaches and depression would have anomalous electrical activity predictive of the onset of clinical symptoms. Methods for prediction of epileptic seizures have been published by Elger and Lehnertz (in Elger, C. E., and Lehnertz, K., xe2x80x9cSeizure prediction by non-linear time series analysis of brain electrical activity,xe2x80x9d Eur. J. Neurosci. 1998 Febuary; 10(2): 786-9, and Osorio, Frei and Wilkinson (in Osorio, I., et al., xe2x80x9cReal-time automated detection and quantitative analysis of seizures and short-term prediction of clinical onset,xe2x80x9d Epilepsia 1998 June; 39(6): 615-27).
Maurer and Sorenson in U.S. Pat. No. 4,019,518 describe a combined internal/external system for electrical stimulation of the body with biphasic pulses but do not describe any means of detecting neurological events. Fischell in U.S. Pat. No. 4,373,527 describes a programmable medication infusion system but does not anticipate its use in response to a detected neurological event.
More recently, a device has been approved for human use to stimulate the vagus nerve in a continuous fashion with the objective of decreasing the rate of epileptic seizures. Clinical reports on such devices indicate only a modest degree of success in that only 50% of the patients experience a greater than 20% reduction in the rate of epileptic seizures. Another device that has been recently introduced into clinical practice utilizes intermittent or continuous stimulation of the thalamus for the treatment of involuntary motion disorders such as Parkinson""s syndrome. Neither of these two open-loop devices described above is highly effective for the treatment of a neurological disorder such as epilepsy, and neither anticipates the use of decision making in order to optimize a response to terminate the precursor of a neurological event or the neurological event itself; nor does either device allow for the recording of EEG signals. In addition, both known devices use stimulation frequencies above 10 Hz, which for the reasons set a forth in detail below, are not optimal.
Fischell et al in U.S. Pat. No. 6,016,449, which is incorporated herein by reference, teaches a fully implantable neurostimulator capable of responsive treatment of neurological disorders. However, Fischell does not discuss in detail the advantageous use of low frequency stimulation as a means of inhibiting epileptiform activity.
It is well known that slow wave potentials in the brain are often inhibitory in nature yet all known stimulation attempts to treat epilepsy in humans have used relatively high frequency stimulation, in most cases greater than 20 Hz. These higher frequencies, while effective for a brain mapping type procedure, have significant potential to induce epileptogenic activity. In fact, Hallett in xe2x80x9cTranscranial magnetic stimulation and the human brain,xe2x80x9d Nature, Vol. 406, Jul. 13, 2000, states that while xe2x80x9crapid repetitive transcranial magnetic stimulation (rTMS), at frequencies of 5 Hz and higher, will transiently enhance motor excitability . . . slow rTMS, at 1 Hz will transiently depress excitability.xe2x80x9d
There is good evidence that slow wave activity is inhibitory in the central nervous system of man (Staton, R. D. et al., xe2x80x9cThe electroencephalographic pattern during electroconvulsive therapy: V. Observations on the origins of phase III delta energy and the mechanism of action of ECT,xe2x80x9d Clin. Electroencephalogr. 1988 October; 19(4): 176-198 and animals (Buzsaki, G. et al., xe2x80x9cDepth profiles of hippocampal rhythmic slow activity (xe2x80x98theta rhythmxe2x80x99) depend on behaviour,xe2x80x9d Electroencephalogr. Clin. Neurophysiol. 1985 July; 61(1): 77-88) including such stimulation applied to the hippocampus (Leung, L. S. et al., xe2x80x9cTheta-frequency resonance in hippocampal CA1 neurons in vitro demonstrated by sinusoidal current injection,xe2x80x9d J. Neurophysiol. 1998 March; 79(3): 1592-6). These slow waves may be at theta frequencies (4 to 7 Hzxe2x80x94Buzsaki et al. 1985), delta frequencies (1 to 3 Hzxe2x80x94Staton et al. 1988), or even at less then 1 Hz (Contreras, D. et al., xe2x80x9cCellular basis of EEG slow rhythms: a study of dynamic corticothalamic relationships,xe2x80x9d J. Neurosci. 1995 January; 15(1 Pt 2): 604-22). Psatta et al. (in xe2x80x9cControl of chronic experimental focal epilepsy by feedback caudatum stimulation,xe2x80x9d Epilepsia 1983 August.; 24(4): 444-54) describe successful ictal spike depression by 5 Hz stimulation of the caudate nucleus (CN) in cat brains. The article also states that stimulation of the thalamus, mesencephalic reticular formation or hypothalamus was not effective. Finally, Hallett (in xe2x80x9cTranscranial magnetic stimulation and the human brainxe2x80x9d Nature 2000; 406 (July 13): 147-150) discusses the inhibitory effects of low frequency pulsing from a transcranial magnetic stimulator.
The present invention includes transcranial stimulation, or direct brain stimulation from multiple electrodes, in either an open or closed-loop system for the treatment of certain neurological disorders such as epilepsy, migraine headaches and Parkinson""s disease. A purpose of the present invention is to overcome the shortcomings of all known devices for the treatment of such disorders. Specifically, the present invention utilizes slow wave potentials (low frequency stimulation in a range of approximately 1 to 10 Hz) to prevent or abort a neurological event.
One embodiment of the present invention envisions a multiplicity of brain electrodes placed either within the brain, on the surface of the brain itself, or on the dura mater that surrounds the brain. Some or all of these brain electrodes may be used to directly detect an abnormal neurological event such as an epileptic seizure, or they may be used to detect a pattern of electrical activity that precedes or accompanies an abnormal neurological event. A stimulation signal can also be applied to any one, several, or all elements of such an electrode array. The is stimulation signals sent to each electrode may be identical or they may be programmed to differ in amplitude, frequency, waveform, phase and time duration. It is also envisioned that sensing electrodes may be entirely separate from the electrodes used for responsive stimulation.
It is also envisioned that appropriate selection (i.e., location) of electrode sites can be used to enhance the reliability for detection and termination of a neurological event. Thus, the present invention envisions enhancement of detection by the use of the spatial domain as it applies to the positioning of detection and treatment electrodes.
A specific capability of this system is to provide electrical stimulation to a specific portion of the brain as the means of stopping a neurological event. It is believed that the earliest possible detection of a seizure and treatment of aberrant electrical activity from an epileptic focus has the highest probability of aborting the occurrence of a full seizure. It is envisioned that either through specific placement of treatment electrodes or by adjusting the phase of signals applied to an array of electrodes, stimulation can be directed to the location(s) within the brain that offer the highest probability of stopping the seizure. Detection of an abnormal neurological event would allow detection of specific but apparently normal patterns of electrical activity, which are reliable producers of the abnormal event; stimulation during the appearance of such patterns may prevent it the occurrence of the event.
A novel aspect of a preferred embodiment of this invention is that the entire implantable portion of this system for treating neurological disorders is implanted under the patient""s scalp or An intracranially. Such placement will either have the device located between the scalp and the cranium or the within a hole in the cranium. Because of size constraints, the intracranial location is the preferred embodiment.
The implantable portion of the system includes: (1) electrodes that lie in close proximity to or actually within the brain, (2) a control module that contains a battery and all the electronics for sensing, recording and controlling brain activity, (3) electrically conducting wires that connect the control module to the electrodes, (4) a buzzer providing an acoustic signal or electrical xe2x80x9cticklexe2x80x9d indicating that a neurological event has been detected, and (5) an input-output wire coil (or antenna) used for communication of the implanted system with any and all external equipment. The battery that provides power for the system and an electronics module are both contained within a metal shell that lies, in one embodiment, under the patient""s scalp. The metal shell, which contains the electronics module and the battery collectively, forms the control module.
All electrodes connect by way of electrically conducting wires to electrical terminals that are formed into the metal shell. The electronics module is electrically joined to the brain electrodes by way of the shell""s electrical terminals, which are electrically joined to the wires that connect to the brain electrodes.
An important aspect of the preferred embodiment of this device is the fact that the shell containing the electronics module and the battery, i.e. the control module, is to be placed in the cranium of the skull at a place where a significant volume of bone is removed. By placing the entire system within the cranium, (as opposed to having some wires extending into or through the patient""s neck to a control module in the chest) the probability of wire breakage due to repeated wire bending is significantly reduced. However, the present invention also envisions the placement in the chest or abdomen of a control module if a large battery or a large volume electronics module dictates such a large size for the control module that it cannot be conveniently placed within the cranium. Such a thoracic or abdominal placement of a control module would typically require wires to be run through the patient""s neck.
The present invention also envisions the utilization of an intracranial system for the treatment of certain diseases without placing wires through the neck. Specifically, an alternative embodiment of the invention envisions the use of electrodes in or on the brain with an intracranial control module used in conjunction with a remote sensor/actuator device implanted elsewhere in the patient""s body. For example, blood pressure could be sensed with a threshold of, for example, 150 mm Hg, and if that pressure is exceeded, a signal transmitted by electrical conduction through the body from the remote sensor/actuator device could be received at the control module, which would initiate brain stimulation in such a way as to reduce the blood pressure. Conversely, if the brain perceives pain and generates a corresponding signal detectable by the intracranial control module, a signal could be sent by electrical conduction through the body to the remote sensor/actuator device, which would provide responsive electrical stimulation to locally stimulate a nerve, thereby reducing the perception of that pain. In still another embodiment, if a precursor of an epileptic seizure is detected, the remote sensor/actuator could be used to electrically stimulate one or both vagus nerves so as to stop the epileptic seizure from occurring. Such a remote device could be located in the trunk of the patient""s body. In an embodiment of the invention, a remote sensor/actuator may be used to deliver instantaneous, intravenous, intraperitoneal, subdural or intraventricular (of the brain) therapeutic chemicals, including medication, neurotransmitters and ionic substances, alone or in conjunction with electrical stimulation. Such a remote sensor/actuator is disclosed in the above referenced U.S. Pat. No. 6,016,449 by Fischell et al.
It is also envisioned the ideal stimulation to prevent or abort a neurological event has a low frequency (e.g., 1 to 8 Hz) that would resemble slow wave inhibitory potentials and be significantly less likely to induce epileptiform activity. In one embodiment of the invention, the stimulation waveform is substantially sinusoidal and has minimal higher-order harmonics, and hence little energy above the fundamental frequency. In an alternative embodiment, the low frequency stimulation comprises a sequence of short duration biphasic pulses having a repetition rate of less than about ten pulses per second (10 Hz). Such stimulation could be applied to the caudate nucleus or other structures of the brain, including the hippocampus. As patients suffering from Parkinson""s have an extremely low incidence of epilepsy and one manifestation of Parkinson""s is characterized by a 5 Hz electrical oscillation that begins in the Thalamus, it is conceived that low frequency stimulation of the Thalamus could, in fact, be inhibitory to epileptiform activity. Such stimulation could be responsive to the detection of a precursor to a clinical seizure or the epileptiform activity from the seizure itself. Alternately, periodic slow wave stimulation applied without detection could prevent the brain from generating seizure activity. Although epilepsy is currently believed to be the most applicable use of such slow wave stimulation, it could also be successful for migraines, pain, tremor, Parkinson""s, depression or other neurological disorders.
It is also envisioned that while the standard treatment would have a constant amplitude for the duration of the low frequency stimulation, it may be advantageous to have the amplitude begin high and decrease over the duration, begin low and increase over the duration, or vary according to any desired treatment plan. The typical duration of low frequency stimulation that would be used to stop a neurological event would be between 100 ms and 10 seconds.
Another embodiment of the present invention that would be significantly less invasive involves the use of Transcranial Magnetic Stimulation (TMS) from an external coil TMS stimulator. Such a device could be incorporated into a bicycle type helmet and could be used at the time a pre-event aura is sensed by the patient. Alternately, such an external system could be used in a repetitive or continuous mode for patients with serious disorders who often wear protective helmets. A TMS device could be extremely effective if it is pulsed on and off at frequencies below 10 Hz.
Thus it is an object of this invention to provide appropriate slow wave stimulation of the human brain in response to a detected neurological event in order to cause the cessation of that neurological event. The pattern and frequency of stimulation can be modified to provide optimal control of the unwanted neurological event in each patient.
Another object of this invention is to use periodic slow wave stimulation of the brain to treat neurological disorders.
Another object of this invention is to use continuous slow wave stimulation of the brain to treat neurological disorders.
Still another object of this invention is to have a system of electrodes connected by wires to a control module, the entire system being placed under the scalp or intracranially, and being substantially contained within an opening in the cranium.
Still another object of this system is to have essentially no flexure of interconnecting wires so as to enhance system reliability.